Field of the Invention
The present invention relates to a facsimile apparatus, a control method thereof, and a storage medium.
Description of the Related Art
A method of performing facsimile (FAX) communication using an IP network has been established in recent years. In Internet facsimile (IP FAX) communication using an IP network, SIP (Session Initiation Protocol) is used as a call connection protocol, and T.38 protocol is used in data communication. In the IP FAX communication using T.38 as well, capability exchange is done by exchanging a DIS (Digital Identification Signal) and a DCS (Digital Command Signal) defined by T.30. A receiver sends the capability declaration of the receiver to a transmitter by a DIS. The transmitter selects a mode to be used for communication based on the DIS within the range of the capability of the transmitter, and notifies the receiver of the result by a DCS. A bit representing whether the receiver/transmitter is a device (IAFD: Internet Aware FAX Device) capable of high-speed communication by the network (NW) speed is defined in the DIS/DCS. The network speed here indicates a speed higher than the speed of G3 FAX communication. A device (for example, a gateway apparatus connected to a G3 FAX apparatus) that can execute facsimile communication via an IP network but supports only G3 FAX communication via an analog line is not applicable to the above-described device capable of high-speed communication. At the time of IP FAX communication, when the devices know that they have the IAFD mode by capability exchange using the DIS/DCS, the communication is performed at the network speed by a DCS while neglecting the selected speed value. Since communication is done via the IP network, as described above, communication at a high speed as compared to conventional G3 FAX can be performed.
On the other hand, the T.38 protocol also defines ECM (Error Correction Mode) communication capable of correcting errors in image data that has failed in reception and Non-ECM communication that omits an intermediate procedure by prohibiting recovery (error correction), like G3 FAX. In ECM communication, image data is divided into HDLC (High-level Data Link Control procedure) frames, and a block including 256 frames at maximum is transmitted. When all frames are normally received, and preparation for reception of the next block is completed, the receiver returns an MCF (Message Confirmation) response. In ECM communication, the size of one block is predetermined to about 64 KB at maximum. If the MCF response cannot be returned immediately, flow control of 1 min is allowed by a T5 timer. That is, a delay of 1 min can be added to the time limit for the MCF response. Hence, ECM communication does not suffer an error caused by a late MCF response.
In Non-ECM communication, however, the image transmission unit is not a block but a page. Additionally, flow control of 1 min as in ECM communication is not defined as a protocol. For these reasons, it may be impossible to return the MCF response (impossible to return the response in time). As a conventional technique related to time adjustment for enabling a receiver to return the MCF response within a prescribed time in Non-ECM communication, Japanese Patent Laid-Open No. 2001-298551 discloses a technique related to minimum transmission time setting of FAX communication defined by ITU-T T.4 recommendation.
However, the conventional technique has a problem to be described below. For example, T.30 recommendation defines that a transmitter must set the minimum transmission time of DCS to 0 ms in communication between IAFDs. This aims at avoiding a case where a given fill as a bit string of 0 is inserted to the end of small line data in accordance with the NW speed, and an enormous quantity of dummy data is sent to the IP network. Hence, in communication between IAFDs, time adjustment by the minimum transmission time as in G3 FAX cannot be used. In Non-ECM communication between IP FAX apparatuses, the problem that the MCF response cannot be returned within the prescribed time remains unsolved. On the other hand, if IAFD declaration is always prohibited to avoid this problem, the speed of ECM communication also undesirably lowers.